1. Field of the Invention
The present invention relates to an acceleration sensor adapted for use in a seatbelt system for protecting an occupant of a vehicle in an emergency situation of the vehicle.
2. Description of the Prior Art
In vehicles such as automobiles acceleration sensors are sometimes used to prevent seatbelts from being unwound from a webbing retractor during emergency situations.
In such seatbelt systems, the webbing fastened about the occupant is retracted in layers and stored within a webbing retractor fixed to the vehicle body. The acceleration sensor present within the webbing retractor allows the webbing to be unwound in an ordinary running situation of the vehicle, so that the occupant can change his attitude voluntarily. However, in an emergency situation of the vehicle, this acceleration sensor prevents the webbing from being unwound from the webbing retractor, so that the occupant is safely restrained by the webbing.
In the ordinary running situation of the vehicle, the ball remains in a stop position in the acceleration sensor. However, when an acceleration of more than a predetermined value acts on the acceleration sensor, the ball ascends a slope formed within the acceleration sensor and triggers an actuator disposed on the ball, thereby stopping the webbing from unwinding out of the webbing retractor.
Unfortunately, such prior art acceleration sensors are not without shortcomings. For example, when the vehicle runs on a rough road, the ball may be slightly moved from its stop position due to vibration, so that in some cases the web-breaking actuator is pushed up, or actuated, by the ball. This actuator may in turn engage a ratchet wheel in the webbing retractor, thereby preventing the unwinding of the webbing, which in turn results in discomforture to the occupant restrained by the webbing.